Quantitative assessment of compositional effects on molybdenum solubility in nuclear waste glasses

The limited solubility of MoO 3 in conventional borosilicate waste glasses can promote the formation of a molybdate-rich molten salt phase, which compromises both waste form durability and melter integrity. To avoid the accumulation of separated phases during vitrification of high-level liquid waste (HLLW), it is crucial to develop glass matrices with enhanced MoO 3 solubility. However, such development remains a challenge due to the absence of quantitative methods for evaluating the tolerance of glass compositions to molybdenum. In this study, this issue is addressed by proposing a method to quantify MoO 3 solubility in borosilicate glasses and compiling a dataset of 143 crucible-scale measurements. Furthermore, an empirical model was developed to predict MoO 3 solubility as a function of glass composition, and independent validation confirms its applicability to HLLW glasses. Although further data can improve accuracy, this model provides quantitative insights into compositional effects. The model-predicted effects of key components align with general trends previously reported in the literature. Notably, B 2 O 3 , Li 2 O, ZnO, V 2 O 5 , and CaO enhance MoO 3 solubility, whereas Na 2 O and Al 2 O 3 exhibit the reverse effect.